Been working on a project for a while and now my latest saves get a ‘Error has been encountered while trying to load a tool. Loading has been aborted.’
I noticed the file in question went over 2GB as a ZPR file. Is there a limit? Is 2GB insane? I have around 20-30 subtools.
Save your subtools separately.
You can then load/append them to any project as needed.
I rarely save .zpr files.
For your .zpr file, I’m guessing you have “Save Undo History” enabled.
I’d turn that off if you don’t really need it - that’s probly what’s increasing the file size and causing subtool load issues. It’s trying to load the undo histories for ALL of your subtools.
Obviously, without undo history enabled, you’ll want to save versions of your subtools if you want to go back to earlier versions.
Yeah, I went from saving ztls to being told to save zpr as that saves your material. Back to ztools then. What is the purpose of ever saving a zpr?
I save both zpr file and ztls to various folders all over the place. Think of a project as a ‘scene’. Place your objects(subtools)
and then you can better arrange and set your ‘camera’ for a render. I load various other objects in after working with just them and saving previously. Undo history would account for large file size as has been mentioned. As large as you stated can be a problem 
Happy ZBrushing 
Yeah, I went from saving ztls to being told to save zpr as that saves your material. Back to ztools then. What is the purpose of ever saving a zpr?
It comes down to personal preference and workflow.
If I knew I was going to want to do a timelapse, I’d save a zpr with undo history. As Doug mentioned, if you set up your scene with lights, materials, background, etc you might save a zpr. I’d still consider not including undo history unless you really need it.
Thanks for the info, have disabled undo from now on unless I find myself needing it. Doubt I ever would, as long as undos are available in my current session that’s all I need.
I save .zprs frequently when I have a number of separate tools I want to be able to work back and forth on without loading all the time. Loading them separately each session is a chore. Also if you ever make a change to a default material, you must save that material and manually reload it every time unless you save as a project.
I regularly work with many dozens of subtools for combined polycounts in the hundreds of millions, and have never exceeded a gb in file size. As has already been pointed out, it’s saving the undo history that’s the killer. I would only ever do that in special circumstances.
so this may be a silly question, but how do you guys keep your files sizes so low, Spyndel you mentioned that your subtools an be in million poly range, my tools can also be in thi range, each one in the millions once i ad fine details, so when i save (without undo history) my file size jumps up.
If i save each tool at the lowest subdivision, does this make the file size less, than if i saved at the highest??